Human beings hear and perceive high pitch and low pitch sounds unevenly. For example, when listening to a 200 Hz tone and a 1000 Hz tone that are produced at the same sound pressure level (SPL), the latter is perceived to be much louder. This is also referred to as perceiving audio loudness with a non-linear, frequency-dependent relationship, relative to measured SPL. A technique referred to as loudness compensation aims to correct for such non-linear, frequency dependent perception of sound, by equalizing or balancing the spectral content of an audio signal. The compensation is typically applied to an audio signal during playback, in response to for example an on/off switch that a user can manually turn on, to change the levels of the high and low frequencies relative to the mid frequencies, so that for example at high SPLs the highs and lows are turned down. Loudness compensation may also be automatic, based on detecting the current user volume setting and in response boosting the low frequencies at low volume settings or attenuating them at high volume settings. Another frequently encountered issue during audio playback is that the user may need to manually adjust an equalizer or the volume setting, each time a different type of song is being played, or a different audio programming channel has been selected.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.